The present invention relates to an image forming apparatus which is suited to read the images of a manuscript and record the read images onto a recording sheet with high quality.
In a conventional copying machine, including an automatic manuscript feed device, when an operator sets a plurality of manuscript sheets in a manuscript tray and uses an operational panel on the machine to input a copy instruction, the manuscript sheets will be automatically fed one by one onto a platen glass. When the sheets are on the platen glass, the images of the manuscripts are read after which the sheets are delivered one by one to a discharge tray. Also, in a conventional copying machine, including an automatic manuscript device which copies both sides of a manuscript sheet, a guide member referred to as a "lead register", is provided at right angles to the feeding direction of the manuscript. The lead register causes the manuscript sheet to butt the end portion of the platen glass to regulate the position of the sheet. In this case, when the manuscript is delivered from the manuscript tray onto the glass platen, initially, images formed on the first surface of the manuscript sheet are read first. Then, if the lead register is lowered below the surface of the platen glass by a drive mechanism, the manuscript sheet is delivered through the end portion of the platen glass to a reversed delivery passage, where the front and back sides of the manuscript are mutually reversed. Then, the manuscript sheet is fed onto the platen glass. When images formed on the second surface of the manuscript sheet are read. Finally the manuscript sheet is delivered to the discharge tray.
To read the images of the manuscript sheet on the platen glass, a light is radiated onto the manuscript sheet from below the platen glass so that reflected light may be read by an image pickup device to generate image signals. In this situation image processing is performed on the image signals and is referred to as edge erasing processing. During edge erasing processing, the edge portion of the manuscript sheet within a range of 2 to 3 mm from the end portion of the manuscript is not recorded onto a recording sheet.
Furthermore, in the conventional copying machine having a lead register, because the light is blocked off by the lead register, a black stripe or shadow is generated inside the edge erased portion. Also, the optical path length of the light passing through a gap between the platen glass and lead register or the end portion of the platen glass is different from the optical path length of the light passing through the lower surface of the platen glass. Consequently, the light from the light source cannot be uniformly radiated onto the end portion of the manuscript sheet abutting the lead register. As a result, a black stripe or shadow is generated inside the edge erased portion. Furthermore, if the amount of the edge erasure is increased, the range lacking the image will also increase, depending on the size of the lead register and the thickness of the platen glass.
Furthermore, when attempting to copy a manuscript sheet using increased magnification, the influences of the lead register and the end portion of the platen glass are correspondingly expanded thereby increasing the range in which the image quality deteriorates, and cannot be dealt with by the edge erasing processing.